1. Field of the Invention
The present invention relates to methods for the production of golf balls. More particularly, the present invention relates to methods of compression molding of a golf ball having a core, a reinforcing layer and a cover.
2. Description of the Related Art
Golf balls are formed by compression molding or injection molding. When golf balls are formed by compression molding, a core and two pieces of a half shell comprising a thermoplastic resin composition are placed into a mold. This resin composition flows within the mold by being heated and compressed. Excess resin composition flows out from a parting line of the mold. A cover is obtained by curing of this resin composition.
Flight performances and control performances are demanded for golf balls. A variety of golf balls have been proposed in an attempt to achieve both the flight performance and the control performance. For example, U.S. Pat. No. 5,823,890 discloses a golf ball having a cover comprising an inner layer and an outer layer, with the inner layer having higher hardness than the outer layer.
Durability is also required for golf balls. Favorable adhesion between the core and the cover enhances durability of the golf ball. U.S. Pat. No. 6,106,415 discloses a golf ball having an adhesive layer between the core and the cover. In this golf ball, the adhesive layer is responsible for the durability.
In compression molding for golf balls having an adhesive layer, excessive flow of the thermoplastic resin composition of the cover causes damage on the adhesive layer by the flow. When the surface of the core is a thermoplastic resin composition, it is likely that flow of this resin composition of the core is also caused. Excessive flow of the resin composition of the core causes significant damage on the adhesive layer. The damage on the adhesive layer reduces durability of the golf ball.
An object of the present invention is to provide a golf ball, which has a cover and a surface of the core, both comprising a thermoplastic resin composition, and which is excellent in durability.